1. Field of the Invention
This invention relates to an arrangement for the controlled application of adhesives and/or sealants to substrate materials. The invention also relates to the use of this arrangement and to a process for controlling the application of adhesives and/or sealants to substrate materials.
2. Background Art
In many cases, continuous strips of adhesive and/or sealant, for example, have to be applied to a substrate material which is moved in endless form (for example in web form) or in the form of consecutive sections or blanks past an arrangement consisting in principle of an applicator head with an applicator nozzle. In other cases, the same substrate material has to be provided at several points with the same adhesive and/or sealant, continuous strips of adhesive and/or sealant, spots of adhesive and/or sealant, length-limited beads of adhesive and/or sealant or patches of adhesive and/or sealant having to be produced. For example, in the production of packages, webs or blanks of material have to provided with adhesive in the form of so-called glue spots, glue beads, or glue patches for fixing in the positions forming the packages.
In order to dose the adhesives and/or sealants, the applicator heads generally comprise valves which control the supply of the adhesives and/or sealants to the applicator nozzle via electronic control units.
For the majority of applications, it is often desirable to obtain a uniform application pattern and a particular quantity or dose of the adhesive and/or sealant to be applied and, in particular, to monitor the desired dose to be applied.
Application of the adhesive and/or sealant has to be monitored because, for example, blockages in the pipe system, the applicator head, the applicator nozzle, in any filters present or a leak at any point of the machine cannot always be reliably ruled out. Differences between the desired dose to be applied and the dose applied in practice can occur, for example, as a result of production-related variations in the feed pump pressure or through changes in viscosity produced, for example, by changes in temperature. The effect of such variations can be in particular that the quantity of adhesive and/or sealant applied is too small for the necessary bonding and/or sealing of the substrate material. Accordingly, efforts have often been made in the past to counteract such effects by including a so-called safety reserve of the adhesive and/or sealant to be applied in the theoretically necessary dose.
Safety reserves are included in particular in processes where the substrate materials have surfaces that are difficult to bond or seal, for example painted, printed or lined surfaces. The inclusion of a safety reserve is also necessary when the bond is subjected to severe tensile stress. This is the case, for example, when substrate materials are bonded together during a shaping or forming process and have a natural tendency to return to their original shape. This happens, for example, when substrate materials are bonded via edges, as for example in the edge banding of wood. Safety reserves are also included in processes where the sealant or adhesive is required to show high heat resistance, as for example where bonded or sealed substrate materials are filled with hot media. Heat resistance in this context generally means the ability of an adhesive layer permanently to withstand exposure to high temperatures without deformation.
Monitoring whether the required dose of adhesive and/or sealant is present on the substrate material is normally done by random sampling or continuously, for example by visual inspection and/or additionally by a) moisture measurements where the adhesive applied is water- or solvent-based, b) infrared sensors for determining the dose of adhesive and/or sealant applied to the substrate through the heat given off, c) gravimetrically by weighing correspondingly marked substrate materials before and after application of the adhesive and/or sealant, or d) microwave or ultrasound technology for measuring traces of adhesive and/or sealant or layers of adhesive and/or sealant.
The accuracy of the monitoring techniques listed above is not particularly high because of the methods used and additional external influencing factors (for example atmospheric humidity). This is another reason for the normal additional dose of the adhesive and/or sealant to be applied as a safety reserve.
If the adhesive and/or sealant is only applied inadequately, if at all, to the substrate material, rejection of the substrate material is generally the result. If it also taken into account that many processes where adhesives and/or sealants are applied to substrate materials now operate at high speeds, the economic loss attributable to rejects and the machine stoppages they involve caused by cleaning and repair work is considerable.
Accordingly, in order to be able to respond more quickly to interruptions in the application of the adhesives and/or sealants to substrate materials, there are advantages in processes where application of the adhesive and/or sealant is monitored between the storage container (reservoir) for the adhesive and/or sealant and the applicator nozzle and not just on the substrate material. Such processes are known.
EP 0 887 721 A1 discloses a monitoring system in which a monitor periodically collects input signals of a sensor and compares the collected signals with stored alarm limit values. The sensor picks up a characteristic of a liquid flowing through a distributor, for example the liquid nozzle pressure. A pressure sensor integrated in the applicator head measures the static pressure of the liquid with the nozzle closed and the dynamic pressure of the liquid with the nozzle open. When the nozzle is open, the pressure falls in dependence upon the throughflow volume. The measured pressures are compared with the predetermined reference pressures are thus monitored. This process allows conclusions to be drawn as to the correct pump pressure and the throughflow volume in the applicator head. However, the lower the throughflow of the liquid in the nozzle, the smaller the measured pressure difference between the dynamic pressure and the reference pressure. Accordingly, it is not possible to measure an adequate pressure difference where the throughflow of liquid is very small, for example less than 100 mg of liquid.
Utility Model No. 296 20 763.2 describes an adhesive applicator which consists of an adhesive reservoir, a feed pump and an applicator head comprising at least one applicator nozzle. The adhesive reservoir, the feed pump and the applicator head are connected by a pipe carrying the adhesive. At least one sensor for the adhesive volume flow rate between the feed pump and the at least one applicator nozzle is provided. The function of this sensor for the adhesive volume flow rate is to measure the volume of adhesive actually delivered by the feed pump to the at least one applicator nozzle. If in the course of a work cycle the sensor should detect that not enough adhesive, if any, is being delivered, a corresponding monitoring circuit triggers an immediate interruption in production readily discernible to the machine attendant.
The above-described systems monitor the application of adhesives and trigger an alarm in the event of interruptions in application, but are not used to regulate the dosage of adhesives. In addition, neither quantity determination nor density determination of the liquid can be carried out with these systems.
U.S. Pat. No. 5,646,737 discloses an arrangement for applying liquid, preferably photographic materials as coatings. Layer measurement of the applied liquid is possible with this arrangement. The quantity applied is calculated from the layer profile in the x and y directions. The use of an encoder enables the quantity applied to be controlled. However, measurement of the layer presupposes that the coated material is absolutely flat, that the thickness of the material remains absolutely constant and that coating is continuous. Accordingly, this application and measuring arrangement can only be used for surface coating on films or film-like materials.
In at least one embodiment, the present invention avoids the disadvantages of the prior art and improves and simplifies existing processes and machines for the application of adhesives and/or sealants. This includes, in particular, achieving improved monitoring of application, more accurate measurement of the quantity applied and control of the quantity of adhesives and/or sealants applied irrespective of the substrate material, the material surface (for example films, nonwovens, paperboard, wood, etc.) and the form of application (for example surface coating, spiral spray application, spot application, bead application). Accurate measurement of the quantity applied would be possible both with intermittent and with continuous forms of application.
In at least one embodiment, the present invention pertains to an arrangement for the controlled application of adhesives and/or sealants to substrate materials which comprises the following components: a) a reservoir for at least one adhesive and/or sealant, b) a feed pump, c) an applicator head with at least one applicator nozzle, d) a volume throughput sensor, and e) a monitoring unit with an associated data processing program.
The reservoir, the feed pump and the applicator head with at least one applicator nozzle are connected together by a conduit system carrying the adhesive and/or sealant. The volume throughput sensor and the monitoring unit with the associated data processing program are connected together by a pulse transmission line. The monitoring unit with the associated data processing program, the feed pump and the applicator head are connected together by control lines.
In at least one embodiment, the present invention also pertains to a process for the controlled application of adhesives and/or sealants to substrate materials wherein a) the volume throughput of the adhesive and/or sealant is measured by the volume throughput sensor, b) the electrical pulses picked up by the volume throughput sensor are passed to the monitoring unit with an associated data processing program, and c) the monitoring unit with the associated data processing program adapts the dose of adhesive and/or sealant applied to the substrate material in-line by continuous balancing the required and actual values and by actuating the feed pump and increasing or reducing its output accordingly.